The present invention relates to any multiple gas turbine power plant with a primary and secondary fuel source that requires gas turbine start-up and shutdown on secondary fuel. More specifically, the present invention relates to Integrated Gasification and Combined Cycle (IGCC) power plants, and more particularly, to methods and systems for removing or returning gas turbines from service to vary plant output or facilitate maintenance on a particular unit.
IGCC plants generally use coal gasification, cooling, cleaning, and saturation equipment, balanced with on-site generation of oxygen and nitrogen to produce a primary plant fuel typically known as syngas. At least some known IGCC plants include a plurality of gas turbines that are powered by syngas received from a common gasification source(s). Accordingly, the common gasification source(s) must respond to any change in fuel demands of the turbines during, for example, a shutdown or start-up of one or more of the gas turbines. Generally, a shutdown of one or more of the turbines may be required during times of maintenance or for a reduction of plant output (i.e., turndown) while maintaining operation of the gasification source(s) at full or reduced rates.
Many gas turbines consume syngas to generate power. This process requires initial firing and loading to a predetermined point using a secondary or back-up fuel, such as natural gas or distillate, followed by fuel transfer, completely or partially, to syngas operation. To return IGCC plants to increased output by bringing one or more offline gas turbine(s) back online, syngas must be flared until the fuel flow rate and fuel condition meets the requirements for transfer. Generally, such methods of bringing a unit online and taking a unit offline regularly produce undesirable plant emissions.